EP11 datasheet(9/46 Pages) POWERINT

9 / 46 page

EPR-00011 - 70 W adapter

22-Jan-01

Page 9 of 46

Power Integrations Inc

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voltage at zero load. By lowering the switching frequency, no-load power consumption is

also greatly reduced.

The bias winding is rectified and filtered by D3, R3 and C8 to create a bias voltage to

power the TOP249Y. A 1

µF capacitor is required for C8 to maintain sufficient voltage

during zero to full load transients. Resistor R8 provides leakage inductance filtering to

prevent peak charging. A ceramic capacitor is shown for C8 however for lower cost an

electrolytic type can be used.

Common mode choke L3 and capacitor C12 attenuate common-mode emission currents

caused by high-voltage switching waveforms on the drain side of the primary winding and

the primary to secondary capacitance. Inductor L2 in conjunction with C5, C15 and C16

attenuate differential-mode emission currents caused by the fundamental and harmonics

of the primary current waveform.

Capacitor C16 provides a high frequency bypass of C7 which shortens the loop formed

by these high frequencies passing through the transformer primary and thus reduces

both the differential and common mode conducted noise.

Frequency jitter is employed by the TOPSwitch-GX family to reduce the conducted noise

as measured for both the CISPR and EN standards (see section 12)

Capacitor C17 filters internal MOSFET gate-drive charge current spikes on the

CONTROL pin and together with R11 and C11 determines the auto-restart frequency.

EP11 Datasheet(PDF) 9 Page - Power Integrations, Inc.